The present invention relates generally to liquid crystal displays, and more particularly, to an off-axis holographic color filter, and a full-color liquid crystal display employing the off-axis holographic color filter.
U.S. Pat. No. 4,807,978 issued Feb. 28, 1989 and assigned to the assignee of the present invention discloses a technique of using three layers of holographic microlenses to separate incident white light into red, green, and blue components focused on the appropriate elements of a liquid crystal device. The invention of U.S. Pat. No. 4,807,978 was primarily concerned with providing illumination to a transparent liquid crystal device and did not consider the effects of the holographic elements when used with a reflective liquid crystal display device.
In a projection display system with a transparent liquid crystal device, the light separated and focused by the holographic elements passes through the liquid crystal spatial light modulator and then continues on to the projection optical system. On the other hand, in a projection display system with a reflective spatial light modulator, the image reflected from the spatial light modulator passes through the holographic elements a second time before reaching the projection optical system.
Prior art techniques used to form a full color projected image were (a) to use three spatial light modulators to create separate red, green and blue images and then superimpose the images by means of color selective beamsplitters, or (b) to use a single spatial light modulator device with a mosaic of absorptive filters to divide the device into red, green and blue picture elements.
Accordingly, it is an objective of the present invention to provide for an off-axis holographic color filter, and a full-color liquid crystal display employing the off-axis holographic color filter.